From d98f46ce647846b0aa30b2e16a30fd4e152a1bf5 Mon Sep 17 00:00:00 2001
From: Carlos Maiolino <cem@kernel.org>
Date: Thu, 10 Jul 2025 22:55:07 +0200
Subject: Add new code

Signed-off-by: Carlos Maiolino <cem@toxiclabs.cc>
---
 Algorithms/linked_list.c | 177 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 177 insertions(+)
 create mode 100644 Algorithms/linked_list.c

(limited to 'Algorithms/linked_list.c')

diff --git a/Algorithms/linked_list.c b/Algorithms/linked_list.c
new file mode 100644
index 0000000..16bf24b
--- /dev/null
+++ b/Algorithms/linked_list.c
@@ -0,0 +1,177 @@
+/*
+ * Copyright (c) Carlos Maiolino <carlos@maiolino.me>.
+ * All Rights Reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it would be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write the Free Software Foundation,
+ * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
+ */
+
+ /* This is a simple example of double linked lists I wrote for fun
+  * Because I had nothing better to do :)
+  */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+struct list_item {
+	int key;
+	struct list_item *prev;
+	struct list_item *next;
+};
+
+struct list_item *list_add(struct list_item *HEAD, int key)
+{
+	struct list_item *item = malloc(sizeof(struct list_item));
+
+	if (!item)
+		goto err_out;
+
+	item->key = key;
+	item->prev = NULL;
+
+	/* list is empty, just asign this item as HEAD */
+	if (!HEAD) {
+		item->next = NULL;
+		HEAD = item;
+		return HEAD;
+	}
+
+	item->next = HEAD;
+	HEAD->prev = item;
+	HEAD = item;
+	return HEAD;
+
+err_out:
+	return NULL;
+}
+
+void list_del_by_item(struct list_item **HEAD, int i)
+{
+	struct list_item *item = *HEAD;
+
+	for (; i > 0; i--) {
+		if (item) {
+			item = item->next;
+		} else {
+			printf("Can't free an inexistent item\n");
+			return;
+		}
+	}
+
+	/* if this is the last item, item->next is already NULL */
+	if (item->prev)
+		item->prev->next = item->next;
+	else {
+		*HEAD = item->next;
+	}
+
+	if (item->next)
+		item->next->prev = item->prev;
+
+	free(item);
+	return;
+}
+/*
+int list_del_by_key(list, key)
+int list_search(list, key)
+*/
+
+void print_list(struct list_item *HEAD)
+{
+	struct list_item *iter = HEAD;
+
+	if (!HEAD) {
+		printf("List is empty\n");
+		return;
+	}
+
+	if (HEAD->prev != NULL) {
+		printf("Item is not the head of the list\n");
+		return;
+	}
+
+	while (iter) {
+		printf(" %d", iter->key);
+		iter = iter->next;
+	}
+	printf("\nEND OF LIST\n");
+}
+
+void print_node(struct list_item *item)
+{
+	int *val = &(item->key);
+	printf("NODE=  %p \n", item);
+	printf("    .prev = %p\n", item->prev);
+	printf("    .next = %p\n", item->next);
+	printf("    .key  = %p\n", &(item->key));
+	printf("    .key  = %d\n", *(&(item->key)));
+	printf("    .key  = %d\n", *val);
+}
+
+void debug_list(struct list_item *HEAD)
+{
+	while (HEAD) {
+		print_node(HEAD);
+		HEAD = HEAD->next;
+	}
+}
+
+int main(void)
+{
+	/* Init list head */
+	struct list_item *HEAD = NULL;
+	int val;
+	char cmd;
+
+	while (1) {
+		printf("Select option: ");
+		scanf(" %c", &cmd);
+
+		switch (cmd) {
+			case 'a':
+				printf("Add value: ");
+				scanf(" %d", &val);
+				HEAD = list_add(HEAD, val);
+				break;
+			case 'd':
+				printf("Item to delete (starting on 0): ");
+				scanf(" %d", &val);
+				if (HEAD)
+					list_del_by_item(&HEAD, val);
+				else
+					printf("List is empty\n");
+				break;
+
+			case 'p':
+				print_list(HEAD);
+				break;
+			case 'D':
+				debug_list(HEAD);
+				break;
+			case 'q':
+				goto out;
+			default:
+				printf("a: add to list, d: del item, p: print\n");
+				break;
+		}
+	}
+
+out:
+	while (HEAD) {
+		struct list_item *next = HEAD->next;
+		free(HEAD);
+		HEAD = next;
+	}
+
+	return 0;
+}
-- 
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